Landscape & Ornamentals

BORERS OF PINES AND OTHER NEEDLE BEARING
EVERGREENS IN LANDSCAPES

Pines, spruces, and firs are commonly planted in Indiana
landscapes individually or in groups to create green borders
that mark property lines or protect homes from the wind. When
stressed by adverse environmental conditions these trees
can be attacked and killed by a variety of insects that bore
into trunks and stems. Injury from borers can be reduced by
helping trees protect themselves, recognizing and managing
early signs of borer injury, and sanitation - the removal of borer
infested trees from the landscape.

Helping Trees Protect Themselves

As a group, borers are most successful when they attack
a tree that is stressed due to lack of water or that is planted
under too much shade. When a borer attacks a vigorously
growing conifer (like pine), the tree can physically pitch the
borer out of the trunk in a flow of sap. Under full sun conditions,
healthy trees have enough energy reserves to produce
poisons that can kill many of the infectious diseases that can
be spread by borers. Trees that are planted properly in the
correct location and provided water during drought are most
capable of defending themselves.

Recognizing and Managing Borer Injury

Borers that feed in the trunk produce a random pattern of
holes in the bark (Figure 1). They can be distinguished from
those produced by feeding woodpeckers and sapsuckers
which make holes in a straight line (Figure 2).

Pests of Live Trees

Bark beetles (Figure 3) are among the more common
boring insects detected in declining evergreens and spruce
in urban and rural areas. Symptoms include holes as thick as
a pencil lead along the main trunk and major limbs. Although
there are many bark beetles in our region, their life cycles are
similar. Once beneath the bark, adults lay eggs that hatch
into small grubs that bore beneath the bark. Grubs eventually
hatch into adults that re-infest the declining tree. Often, more
than 100 beetles per square foot of bark can emerge from
declining trees, carrying a blue-stain fungus that attacks the
plant vascular system. This fungus can be passed to new
trees when they are attacked by the adult bark beetles. Bark
beetles on evergreens have several generations of adults
that fly from mid April through mid September.

These beetles can be controlled through sanitation activities
in the winter and applications of insecticides to the tree
trunk during the adult flight period.

Pine sawyer beetles (Figure 4) are often reported on
white and Scotch pine. Infested trees have holes about 3/8”
wide that produce a tremendous amount of finely shredded
wood shavings and brown grainy excrement. Peeling back
the bark of affected trees during the spring and fall reveals
3/4” long white round-headed borers with strong brown
mandibles. In July, it is actually possible to hear the grubs
chewing beneath the bark. The first beetles that attack these
trees can carry a roundworm called the "pine wilt nematode"
which can clog the tree's circulatory system so fast that their
needles yellow and wilt before they turn brown. As with bark
beetles and blue-stain fungi, healthy plants are better able to
withstand some attacks. Pine sawyer beetles winter as larvae
and emerge as adults from mid-May through August.

These beetles can be controlled through sanitation activities
in the winter and applications of insecticides to the tree
trunk during the adult flight period.

Zimmerman pine moths (Figure 5) are common pests
of Austrian and Scotch pines and Norway spruce that can kill
tree limbs and tree tops. They are usually found boring into
the trunks of trees near where the branches meet the main
stem. Unlike the previously mentioned pests, these insects
cause the tree to produce a large amount of gummy sap
and sawdust pellets that are most apparent from late June
through early August. Adults emerge from trees from late
July through August and lay eggs in cracks and crevices in
the bark. Young caterpillars feed on bits of bark and pine gum
until they dig shallow pits, where they spend the winter. When
the weather warms in early April, the caterpillar crawls out of
its resting place along the exposed bark surface to where the
branches join the central trunk. Once there, it bores beneath
the bark and produces gummy wounds, sometimes girdling
or killing limbs or tree tops.

These caterpillars can be controlled through sanitation
activities prior to late July and with applications of insecticides
to the tree trunk during early April to kill caterpillars as they
crawl from overwintering sites to bore into the trees.

White pine weevils (Figure 6) are common pests of pines,
Douglas-fir, and spruces. Like trees infested with Zimmerman
pine moths, the central leader and lateral branches can be
curled into a shape that resembles a shepherd’s crook. The
top two to three years of growth can be affected. This pest
can be distinguished from Zimmerman pine moth by lack of
gummy sap and the presence of a tunnel in the central shoot
or small round exit holes on the side. Lateral branches from
the infested tree’s first whorl may also be curled (Figure 7).

In late March or early April, adult females (Figure 7) lay
eggs in twigs, leaving behind a glistening drop of sap. In
early summer, legless (1/4”) white c-shaped grubs can be
found in stems, beneath the bark surface. By late June and
through July, larvae form chip-bark cocoons inside the base
of injured stems. Adults winter in leaf litter and fly to tree tops
to mate when the weather warms in the spring. Females lay
many eggs in terminals, hatching into grubs that bore into
shoots. Legless larvae continue to feed through July, when
they pupate in chip bark cocoons inside the twig. Adults
emerge in August and chew on twigs before overwintering
in the leaf litter.

These weevils can be controlled, in June and July, by
removing and destroying curled branches that contain the
weevils. Applications of borer insecticides to the tree leaders
or imidacloprid to the soil can be effective in early spring to
kill adults attempting to lay eggs.

Pests Found Near Dead Trees and Stumps

Weevil pests that breed in dead or dying pine can stunt
or kill neighboring healthy pine trees. These include the
pales weevil, northern pine weevil, and pine root collar
weevil. Pales and northern pine weevil can also attack pine
seedlings that are planted next to dead stumps to replace
recently killed pines. Management of these pests requires
treating dead stumps with insecticides or waiting two years
to replant next to stumps.

The pales and northern pine weevils are two closely
related beetles that chew on twigs in the fall and spring,
causing twigs to ooze sap and turn brown in early summer.
Adults are black snout-weevils, and the pales weevil (Figure
8) is about 1/2” long with small gold spots, while the Northern
pine weevil is somewhat smaller, with white patches on the
end of its hind wings (Figure 6). Larvae of both species are
white and legless. Adults are attracted to cut pine and mate
on pine stumps when the weather warms in spring. Females
burrow to roots of cut stumps to lay eggs. Larvae feed on
these roots until they pupate in chip bark cocoons and emerge
adults in September. During the summer, adults spend
days in leaf litter and nights feeding on twigs. Adults live
for two years and lay eggs during both summers. Applying
insecticides to the twigs in early September and April can kill
adults attempting to girdle twigs.

Pine root collar weevil (Figure 9) is less common in the
landscape, but can readily kill trees. Adults feed on the bark
near the soil surface and their young feed on root and root
collar. Injured plants produce large amounts of darkened
sap at or near feeding sites that are clearly visible at the soil
line. Partially girdled plants become weak and are subject
to bark beetle attack, while completely girdled plants die and
turn brown. Adults are black snout-weevils, and the larvae
are white and legless. Adults live for two years and lay eggs
both summers. Each year they chew into bark of live trees
and lay eggs in injured sites from May to September. Eggs
laid in spring become pupae or adults by September. Eggs
laid in summer will winter as larvae and become pupae the
following July. Larvae feed on root and are present all months
of the year.

Sanitation

Removing and destroying infested trees help protect
neighboring trees that are still healthy. Burning, or chipping
and burying the trees with borers inside, will kill the borers
before they become adults and can walk, crawl, or fly to
nearby healthy trees.

Sanitation is most effective between Oct. 1 and April 1,
when most of the borers are spending the winter inside trees.
These dying trees also act as traps that lure local borers away
from healthy trees to breed inside them. Sanitation efforts
should be focused on evergreens that have at least half of
their branches containing completely brown needles. Trees
that have declined to this state will not recover and will soon
die. Destroying these trees before April 1 will kill the borers
before they leave to attack healthy trees.

Insecticides for Controlling Borers

Three insecticides are most commonly available for home
landscape use. These include permethrin (e.g., Hi-Yield 38
plus), bifenthrin (e.g., Onyx), and carbaryl (e.g., Sevin XLR).
Susceptible parts of trees should be coated with these insecticides
so that the insect is poisoned while chewing holes to
either enter or exit the tree. Although other insecticides like
imidacloprid (Bayer Tree and Shrub) can be applied to the
soil to kill boring beetles, these materials are not likely to be
effective on dying trees which are unable to take up material
from the soil. Soil insecticides applied in fall and early spring
might be helpful for protecting apparently healthy evergreens
that remain in a planting after dead trees have been removed.

READ AND FOLLOW ALL LABEL INSTRUCTIONS. THIS INCLUDES DIRECTIONS FOR USE, PRECAUTIONARY STATEMENTS (HAZARDS TO HUMANS, DOMESTIC ANIMALS, AND ENDANGERED SPECIES), ENVIRONMENTAL HAZARDS, RATES OF APPLICATION, NUMBER OF APPLICATIONS, REENTRY INTERVALS, HARVEST RESTRICTIONS, STORAGE AND DISPOSAL, AND ANY SPECIFIC WARNINGS AND/OR PRECAUTIONS FOR SAFE HANDLING OF THE PESTICIDE.

April 2016

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This work is supported in part by Extension Implementation Grant 2017-70006-27140/ IND011460G4-1013877 from the USDA National Institute of Food and Agriculture.